International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

Multilingual Technical Dictionary (MTD)
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Term No.Term Name/Term DescriptionAction
6
Accuracy of the mean
The closeness of agreement between the true value and the mean result obtained by applying the experimental procedure to a very large number of times. The smaller the systematic part of the experimental errors which affect the results, the more accurate is the procedure......
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54
Annual-flood peak series
The tabulation or graph in order of decreasing magnitude of the maximum peak floods of each year.
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105
Arithematic mean
The arithmetic mean of a set of values. Generally denoted by a bar, thus :
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107
Consecutive average, Moving average, or Consecutive mean
The mean of a small group of consecutive values, especially annual means, assigned to the middle time-term of the group in the process of smoothing, e.g. 5-year mean......
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109
Geometric mean
If the set of n values are all multiplied together and the nth root is taken, the results are known as the geometric mean (G), viz. G = (x1 . x2 ... x n-1 . xn)1/n .....
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110
Harmonic mean
The reciprocal of the arithmetic mean of the reciprocals of each observation.
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113
Weighted average, or Weighted mean
An average of quantities that attaches a series of weights to it in order to make proper allowance for their relative importance. A value obtained by multiplying each of a series of values by its assigned weight and dividing the sum of those products by the sum of the weights. For example, a weighted arithmetic mean of x1, x2 ... xn with weights w1.....
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114
Root mean square
The square root of the arithmetic mean of the squares of each observation and is given by
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117
Average deviation, or Mean deviation
A measure of dispersion derived from the average deviation of observations from some central value, such deviations being absolute, i.e. without reference to algebric sign......
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129
Mean square
In general, the mean square of a set of values is the arithmetic mean of the squares of their differences from some given value, namely their second moment about that value......
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134
Standardized averages, or Standardized means
A method of allowing or `adjusting` the effects of other variables, or for differences in the composition of the groups that are to be compared, by using a standard set of weights to combine the means of sub-groups into a single mean. Used mainly for the construction of index numbers......
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208
Mean square error of estimate
The square root of the arithmetic mean of the squared deviations between the estimates for different samples and the population parameter under estimation......
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278
Mean consecutive
The mean of a small group of consecutive values, especially annual means, assigned to the middle time-term of the group, in the process of `smoothing`......
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753
Precipitation
The total measurable  aqueous particles of all forms of falling from the atmosphere, including dew, rain, mist, snow, hail and sleet usually expressed as liquid water depth at a given point over a given time.  .....
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754
Convective precipitation
Precipitation resulting from the upward movement of air that is warmer than its surroundings and falls not far from the originating updraft. .....
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755
Cyclonic Precipitation
The precipitation associated with the passage of cyclones.
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756
Orographic precipitation
Precipitation which results from the lifting of moist air over an orographic barrier, such as the windward side of a mountain range......
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757
Antecedent precipitation index
A weighted summation of daily precipitation amounts, used as an index of soil moisture. The weight given to each day’s precipitation is usually assumed to be an exponential or reciprocal function of time with the most recent precipitation receiving the greatest weight. Such indices are used in calculating runoff in numerical watershed models and .....
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758
Maximum probable precipitation
An estimate of precipitation of a given amount and duration derived by a technique of maximization of all contributing factors like moisture content, precipitable water, wind velocity and spatial distribution. It is a value that has extremely low probability of occurrence......
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759
Mean annual precipitation
The average over a period of years of the annual amounts of precipitation.
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760
Weighted mean monthly precipitation
The weighted mean precipitation for each month for a large area derived from the study of the isohyetal map of the area.
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762
Precipitation mass curve
Graph showing accumulated precipitation against time.
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807
Mass rainfall curve, or Mass precipitation curve
A plot of accumulated precipitation against time.
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847
Mean annual runoff
The value of the annual volume of water discharged by the stream drainage of the areausing  sufficiently long record to obtain a fair mean......
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848
Mean monthly runoff
Arithmetic mean of all the individual monthly mean discharges for a named month in a period of record.
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